1. Field of the Invention
The present invention relates to an optical path re-arrangement method for an optical communication network.
2. Description of Related Art
An optical communication network comprises a plurality of routers, a plurality of optical switches, optical fibers connecting the routers and optical switches or connecting two optical switches, and a management device. In the optical communication network, shifting the arrangement of optical paths of the whole optical communication network (known simply as ‘optical path arrangement’hereinbelow) dynamically in order to increase the packet transfer capacity, that is, re-arranging the optical path arrangement has been proposed (See Nonpatent Document 1: Nakahira et al., “Dynamic path switching experiment for maximizing throughput on IP optical GMPLS test-bed network”, OFC2004, Los Angeles, February, 2004, and Nonpatent Document 2: Nakahira et al. “Study of shifting procedure for dynamic optical path arrangement corresponding with traffic” SB2-5, EICEE, March 2004, for example).
The shift (re-allocation) from the currently used optical path arrangement (known hereinafter simply as ‘current path arrangement’ to an optimum optical path arrangement (known hereinafter simply as ‘optimum path arrangement’ is performed by switching the optical switches provided in the optical communication network and by changing the individual optical paths by switching the router settings, for example.
About the methods of shifting (re-allocating) from the current path arrangement to the optimum path arrangement for the whole optical communication network, there is a method that arranges new optical paths by canceling all the optical paths that need to be changed and then using the network resources obtained as a result of the cancellation, for example. Alternatively, there is also a method that makes the shift from the current path arrangement to the optimum path arrangement by arranging new optical paths by canceling half the number of optical paths that need to be changed all together and using the network resources obtained as a result of the cancellation and then arranging new optical paths after canceling the remaining half number of optical paths all together (See Nonpatent Document 2).
However, in the case of the optical path re-arrangement method of the optical communication network of the above prior art example, at the time of the shift of the optical path arrangement, the network resources that can be used decrease temporarily. That is, when the optical paths that need to be changed are canceled, the packets transmitted by the optical paths are transferred to other optical paths and, therefore, congestion and so forth occurs in the other optical paths, routers, and so forth, and there is the risk of a loss of packets occurring.
In the shift of the optical path arrangement, two types of methods, namely methods performed in one stage and methods performed in two stages are executed. Here, performing the shift of the optical path arrangement in one stage involves setting new optical paths after canceling all the optical paths that need to be changed all together. Further, performing the shift of the optical path arrangement in two stages involves dividing the optical paths that need to be changed into two groups, setting new optical paths after initially canceling the optical paths of the one group altogether, and setting new optical paths after canceling the optical paths of the other group altogether.
It is dependent on the constitution of the optical communication network and the state of the network such as traffic in which cases of performing the shift of the optical path arrangement in one stage and performing same in two stages the amount of packet loss decreases. When the shift is made in one stage, although the time required for the shift is short, the optical paths that can be used in the shift decrease. On the other hand, when the shift is made in two stages, there are more optical paths that can be used in the shift than when the shift is made in one stage and, therefore, packet loss is not readily produced. However, because the time required for the shift is longer than in the case where the shift is made in one stage, there is sometimes a larger amount of packet loss as a result.
In the optical path re-arrangement method of a conventional optical communication network, there is no procedure for judging whether the shift of the path arrangement is made in one stage or whether the shift is performed in two stages in accordance with the state of the network. As a result, it has not been possible to make the shift of the optical path arrangement by means of the optimum method with which there is a small amount of packet loss.
The present invention was conceived in view of the above problem and an object of the present invention is to provide an optical path re-arrangement method of an optical communication network that makes it possible to reduce the amount of packet loss during the shift of the path arrangement by judging whether the shift of the path arrangement is made in one stage or two stages in accordance with the state of the optical communication network.